1. Field of the Invention
This invention relates to resonant tunneling devices (RTDs) and more particularly to methods for supplying electrical power to resonant tunneling devices.
2. Background of Invention
Sub-millimeter wavelength microwave oscillators are essential microwave components. They are used as local oscillators within millimeter wavelength radio receivers and as the basic frequency-determining function within millimeter wavelength radio transmitters. Since the possible bandwidth of information impressed on a frequency carrier is proportional to the carrier frequency, oscillators that operate above 1000 GHz (1 Terahertz) would allow unprecedented modulation bandwidth relative to current technology. Typically, field effect transistors, bipolar transistors, impact ionization diodes, and Gunn-effect diodes are used in microwave oscillators, but these devices have inherent frequency limitations due to their size which limits speed due to transit time effects. Resonant tunneling diodes (RTDs) are semiconductor devices with very high intrinsic gain and switching speed and would allow microwave oscillators to be constructed for frequency bands well above 1000 GHz. However, resonant tunneling diode oscillator circuits are very difficult to electrically bias so that the bias circuitry does not resonate with the RTD and produce unwanted modes of oscillation. Reddy et. al. provided one method for properly biasing RTDs in microwave oscillators based on the use of transmission lines and Schottky diodes. REF: M. Reddy, et. al. xe2x80x9cBias Stabilization for Resonant Tunnel Diode Oscillators,xe2x80x9d IEEE Microwave and Guided Wave Letters, Vol. 5, No.7, July 1995. However, this method still allows the parasitic resonances to occur in the power supply circuitry. Therefore there remains the general problem of providing RTD-based circuits that oscillate at ultra high frequency while suppressing lower frequency oscillations.
In accordance with one embodiment of the present invention the problem of providing a low inductance, high capacitance means to supply power is to use a photocell to power and bias the RTD such that essentially no spurious resonances are possible.